WOT vibration and poping
Thread Starter
Pro
Joined: Sep 2012
Posts: 600
Likes: 6
From: Key West Florida
WOT vibration and poping
after installing a set of aftermarket heads my L48 at WOT will make a vibration and a random pop through the exhaust, it did not do this with the old 882 heads, I did go up a jet size on the primaries on the q-jet, just wondering what could cause this, it has patriot performance heads, a comp 12-210-2 cam with .454 lift and 218 duration at .050. Edelbrock 2101 intake, MSD street fire distributer, it only does this at WOT, at partial throttle it runs great and makes plenty of power. im not turning it hard, about 5500rpm. timing is set at 8* BTDC, it has a curve kit in it with the lightest springs. im just wondering if it is a lean condition and should go to a smaller metering rod for the secondary's
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
I'd suspect ignition breakdown first before carb problems. Plugs and/or wires. If the ignition is in top shape then start with carb settings. If it is just at WOT then I'd look at the secondary metering AFTER the ignition is checked out.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Try jetting the primaries back down. They are responsible for most of the initial WOT response and also your part throttle performance.
If the primaries are too rich you can get some stuttering or breaking up at WOT. Not sure about popping. Check your plugs see if they look lean or rich.
Most of the WOT is in the primaries for quite a while until the vacuum secondaries open up then they start metering fuel in. Secondary adjustment can be made to some degree by bending the hanger up for richer and down for leaner. Just a few thousanth's of an inch at a time.
Also your timing sound a little retarded. Maybe more in the 12* to 16* range for initial would be better.
Like casey jones said make sure ignition is in good shape that could be the problem.
If the primaries are too rich you can get some stuttering or breaking up at WOT. Not sure about popping. Check your plugs see if they look lean or rich.
Most of the WOT is in the primaries for quite a while until the vacuum secondaries open up then they start metering fuel in. Secondary adjustment can be made to some degree by bending the hanger up for richer and down for leaner. Just a few thousanth's of an inch at a time.
Also your timing sound a little retarded. Maybe more in the 12* to 16* range for initial would be better.
Like casey jones said make sure ignition is in good shape that could be the problem.
Last edited by REELAV8R; Nov 11, 2013 at 10:54 AM.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
after fire is caused by a lean condition. your new heads may flow 'too well'. the light springs may be causing the curve to come in too soon-check for full advance only after 2500 rpm. lars just posted in another thread that if the secondary air valve is set excessively loose a back fire(maybe your vibration) is the result.
Advanced
Joined: Aug 2013
Posts: 92
Likes: 4
Do not know if that is a points distributor. On my Pontiac, installed new distributor. Points condensor, wires, all that. Soon had poppin at wot, then got slowly worse. Ended up being condensor. That was after changing all else. She still runs good with old condensor in it.
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